1. Field of the Invention
The present invention relates to a thermoplastic resin composition, and more particularly, to a heat-resistant acrylonitrile-butadiene-styrene (ABS) resin composition having improved weld strength, chemical resistance, impact strength, elongation, and wettablility.
2. Description of the Related Art
Generally, a heat-resistant acrylonitrile-butadiene-styrene (ABS) resin having excellent impact resistance, processability, chemical resistance, etc. has been used as interior and exterior materials for automobiles etc., and parts for electric and electronic equipments such as office appliances and home electric appliances. In the case of ABS used as interior and exterior materials for automobiles, a high performance heat-resistant resin having superior heat resistance and various post processing properties is required.
To give heat-resistance in the ABS resin, a method of preparing a heat-resistant ABS by mixing a heat-resistant copolymer with a graft ABS polymer has been widely used. That is, a method of preparing a heat-resistant ABS resin in which a partition or total amount of styrene used in the preparation of a heat-resistant copolymer is substituted with α-methyl styrene having good heat-resistance (U.S. Pat. No. 3,111,501), a method of preparing a heat-resistant ABS resin including an acryl amide compound (European Patent No. 0,330,038), etc. are known in the art.
According to U.S. Pat. No. 3,111,501, in the preparation of a heat-resistant ABS resin, a partition or total amount of styrene is substituted with α-methyl styrene having good heat-resistance. However, due to α-styrene having a lower reaction rate than other monomers, a large amount of monomers are remained, which results in low yield and poor impact strength and heat resistance. When better heat resistance is required for industrial use, an imide-substituted copolymer is blended to prepare the heat-resistant ABS resin. The heat-resistant ABS is prepared using N-phenylmaleimide in the preparation of a heat resistance enhancer (U.S. Pat. No. 4,567,233) or using N-orthochlorophenylmaleimide or an allyl, alkyl, or cyclic substituent (U.S. Pat. Nos. 3,652,726 and 5,726,265). However, these methods have disadvantages of high manufacturing costs.
ABS is mixed with two materials described above, i.e., the heat-resistant copolymer and the imide-substituted copolymer considering heat resistance and cost effectiveness. When mixing the materials, compatibility between the two materials is poor, and thus impact strength and elongation are deteriorated.
The heat-resistant ABS used as interior and exterior materials for automobiles is often subjected to a postprocessing process. A representative example of the postprocessing process is a painting process. In the painting process, when a resin does not have an affinity for a chemical solvent, appearance defects such as pin holes and paint stains are caused. When chemical resistance of the resin is poor, paint cracks are produced.
Furthermore, when a resin does not have an affinity for a chemical solvent, the painting process should be performed several times, resulting in, in particular, waste of chemical solvents and discomfort to workers. In addition, a thick coating of chemical solvents leads to poor coating appearance after it is dried.
The thermoplastic resin composition used as, in particular, a material of automobile lamp housing requires good weld strength in addition to heat resistance and painting characteristics. The weld strength is a property required when a cross section of a molded article is heated to weld to the other molded article, thereby obtaining a final article. A welding surface of the molded article should be clear when separated from a hot plate. However, most rubber reinforced thermoplastic resin compositions conventionally used in the art produce a lot of stings in their welding surfaces when separated from a hot plate, which requires an additional process for removing strings and reduces productivity.